Charged particle beam apparatuses have many functions in a plurality of industrial fields, including, but not limited to, inspection of semiconductor devices during manufacturing, exposure systems for lithography, detecting devices and testing systems. Thus, there is a high demand for structuring and inspecting specimens within the micrometer and nanometer scale.
Micrometer and nanometer scale process control, inspection or structuring, is often done with charged particle beams, e.g., electron beams, which are generated and focused in charged particle beam devices, such as electron microscopes or electron beam pattern generators. Charged particle beams offer superior spatial resolution compared to, e.g. photon beams due to their short wavelengths.
Particle beam optical systems suffer from various types of imperfections, e.g. mechanical manufacturing imperfections, misalignment of optical components, material inhomogenities, imperfections of the electric and magnetic fields used for focusing, aligning and adjusting, electron optical aberrations, contaminations and charging of beam steering components. A good electron optical design aims at minimizing these imperfections by imposing strict tolerances on mechanical manufacturing, material properties and cleanliness and by optimizing the electron optical performance through proper design.
However, with these measures alone the theoretical optical performance will not be obtainable. Therefore, a lot of devices and methods have been devised over the years which allow counteracting the influence of the above mentioned imperfections. Such devices can be, amongst others, dipole deflectors (to correct misalignment between components), quadrupole stigmators (to correct axial astigmatism in the image), heated sample holders and apertures (to avoid contamination and/or subsequent charging), in-situ plasma cleaning (to remove contaminations in the beam line), and the like.
The above mentioned imperfections become more noticeable if resolution improves so that the spot deterioration becomes clearly visible, the beam leaves the paraxial region around the optical axis and experiences higher order aberrations, the beam current is increased, and/or the beam bundle diameter is increased, in order to reduce electron-electron interaction. This makes the beam more sensitive to higher order aberrations that deteriorate the diameter of the focused spot. Further, the above mentioned imperfections become more noticeable if the beam current in the system increases since this also increases the rate of contamination build-up that causes beam instabilities and spot size deterioration.
These critical conditions are all fulfilled in modern electron beam inspection (EBI) columns. Accordingly, it is desirable to provide a device that compensates such influences that limit the performance of the high beam current system. This will improve resolution and make the system less sensitive to mechanical imperfections, contamination and contamination build-up over time since it provides a remedial measure. This would further assist in improving system performance and/or throughput, extending service intervals and lowering of cost of ownership.